best way to do bit masking in winforms

[not_a_commie]

I need to draw (GDI+) rectangles that don't actually overwrite the
background (aka, what was already drawn to the Graphics object) if the
background is approximately black. What is the most efficient way to
do this? I can build up a Region checking each individual pixel
whenever my background image changes. I can then use sub-portions of
this region in my paint method. However, this seems kludgy to me. Any
better options?

 

[Ben Voigt [C++ MVP]]

Can you possibly use GDI for this, which has raster operation codes? In
this case using AND might have the desired effect.

I need to draw (GDI+) rectangles that don't actually overwrite the
background (aka, what was already drawn to the Graphics object) if the
background is approximately black. What is the most efficient way to
do this? I can build up a Region checking each individual pixel
whenever my background image changes. I can then use sub-portions of
this region in my paint method. However, this seems kludgy to me. Any
better options?

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